The ear canal 10 (FIG. 2) is generally narrow and tortuous and is approximately 26 millimeters (mm) long from the canal aperture 11 to the tympanic membrane 15 (eardrum). The lateral part is flexible and referred to as the cartilaginous canal 12 due to the underlying cartilaginous tissue 16 beneath the skin. The medial part, proximal to the tympanic membrane, is rigid and referred to as the bony region 13 due to the underlying bone tissue. A characteristic first bend occurs roughly at the aperture 11 of the ear canal 10. A second characteristic bend 8 occurs roughly at the bony-cartilaginous junction and separates the cartilaginous region 12 and the bony region 13. The dimensions and contours of the ear canal 10 may vary significantly among individuals, but are generally narrow with little space for accommodating miniaturized components therewithin. The ear canal 10 is generally sensitive to touch and pressure, particularly in the deeper region, which can readily experience discomfort, abrasion and trauma with pressure and rigid contact. Abrasion of the skin inside the ear canal 10 due to hearing aid use is common and generally limits insertions to the lateral (outer) portions of the ear canal 19. The lateral portion (away from the eardrum 15) of the ear canal 10 is relatively physiologically more active than the medial portion (toward the eardrum 15), for example produces more sweat and cerumen (earwax).
Placement of a hearing device inside the ear canal 10 is generally desirable for various advantages such as reduction of the acoustic occlusion effect, improved energy efficiency, reduced distortion, reduced receiver vibrations, and improved high frequency response. Placement inside the ear canal 10 may also be desirable for cosmetic reasons, with many of the hearing impaired preferring to wear inconspicuous hearing devices. A canal hearing device can be inserted entirely or partially inside the ear canal 10. In the context of this application, a “canal hearing device” refers to any hearing device with sound delivery inside the ear canal, whether partially or fully inserted therein.
Sealing inside the ear canal 10 reduces the acoustical feedback which may occur when there is acoustic leakage from an output of a receiver of the hearing device to an input of a microphone of the hearing device through an uncontrolled leakage path. Additionally, an acoustic occlusion (amplified self-voice) effect may result from occlusion of the ear canal 10 by the hearing device. Venting of hearing devices is usually required to address aeration within the ear canal 10 and to relieve the acoustic occlusion effect. Conventional hearing devices provide venting by including tubes or channels that connect the ambient air in the atmosphere outside the ear with the residual volume in the ear canal 10 occluded by the hearing device.